The major objectives of our research program are (1) to identify and characterize the gene products of the newly identified oncogene c-kit, (2) to determine how a modified version of this gene v-kit has acquired transforming activity, and (3) to characterize oncogenes in new FeSV strains. The HZ4-FeSV is a new acute transforming feline retrovirus we have recently shown to contain a unique oncogene v-kit. The transforming protein of this virus is a gag-kit fusion protein. The predicted amino acid sequence of v-kit displays features characteristic of tyrosine specific protein kinases, v-fms being its closest relative. c-fms is known to be homologous with the gene specifying the CSF-1 receptor. Because of the close relationship of v-kit with v-fms and PDGFR, we predict that the c- kit gene product is a receptor which is functionally related to the CSF-1 receptor. To gain a deeper understanding of transformation mediated by transmembrane receptor oncogenes a structural and functional analysis of c-kit and v-kit in which similar and dissimilar features of v-kit and v-fms and c-kit and c-fms will be exploited is proposed. In our proposed structural and functional studies of the c-kit gene products we will investigate the expression of c-kit RNA and in order to determine the primary structure of c-kit we will molecularly clone a c-kit cDNA. We will construct a retrovirus expression vector containing the c-kit cDNA in order to investigate the function and significance of domains in c-kit as they relate to transformation by v-kit. By using kit specific antibodies which will be obtained as part of this proposal we will identify and characterize the c-kit protein product(s). Our studies on v-kit mediated transformation will include: the characterization of enzymatic activities associated with the gag- kit protein; investigations of the significance of membrane association of the gag-kit protein in transformation, the significance of c-terminal sequences in v-kit transformation, and the significance of the kit-specific middle domain in transformation.